Using existing source code as third-party code to build new software systems becomes very popular in these days. However, many existing code is keeping on updating during their life circle. Different versions of code, even out-dated, is reused by other software and spreading all over the world. This paper presents an empirical study on the reuse of out-dated third-party source code of several famous open source libraries. Given target source code, using repository mining techniques and file clone detection techniques, we identified the different versions of code in other user projects, and discovered the vulnerability information of the out-dated versions. We also investigated how user projects manage their code. The result shows that a large proportion of open source projects are reusing out-dated third-party code, and many of them are not well managed.